As magnetic recording media there have heretofore been widely used coating type magnetic recording media produced by coating a non-magnetic substrate with a dispersion of a powdered magnetic material such as a magnetic oxide, e.g., gamma-Fe.sub.2 O.sub.3, Co-doped gamma-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, Co-doped Fe.sub.3 O.sub.4, a Berthollide compound of gamma-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, a Co-doped Berthollide compound, and CrO.sub.2, or a magnetic alloy powder mainly containing Fe, Co, and Ni, in an organic binder such as vinyl chloride-vinyl acetate copolymer, styrene-butadiene copolymer, epoxy resin and polyurethane, and then drying the dispersion.
With increasing need for high density magnetic recording in recent years, ferromagnetic metal thin films formed by vacuum deposition, sputtering or ion plating, i.e. a "metal thin film" type recording medium using no binder have attracted attention, and efforts have been made to put such a recording medium into practical use.
In conventional coating type magnetic recording media, generally a metal oxide having a small saturation magnetization is used as a magnetic material, and the volume content of the magnetic material in the magnetic layer is only from 30 to 50%. Therefore, the conventional coating type magnetic recording media have limited use for high output and high density recording media. Furthermore, the conventional magnetic recording media have the disadvantage that the production process is complicated and requires a large-scale incidental facility for recovering solvents and preventing pollution.
The metal thin film type magnetic recording media are advantageous in that a ferromagnetic metal having a higher saturation magnetization than the oxide magnetic materials can be made into an extremely thin flim without using a non-magnetic material such as an organic binder. For higher density magnetic recording, the gap width of the magnetic head for recording and replaying is typically less than 1.0 micrometer, and the depth of the magnetic recording layer in which the recording is made is shallower than with conventional materials.
Therefore, the metal thin film type magnetic recording medium, which can be used throughout the thickness of the magnetic layer thereof for recording of magnetic signals, is extremely suitable as a high output and high density recording medium. Of various processes for the production of metal thin film type magnetic recording media, the vacuum deposition process is advantageous since the rate of film formation is high and the production process is a simple dry process which requires no treatment of waste liquid. In particular, the oblique incidence vacuum deposition process, in which a deposition flow of a magnetic metal is incident obliquely upon the plane of the non-magnetic substrate, has the practical advantage that it can be performed in a simple manner by means of a simple apparatus to obtain a thin metal film having excellent magnetic properties.
To produce a magnetic recording tape by vacuum-depositing a magnetic thin film onto a tape-like non-magnetic substrate, a process as described in Japanese Patent Application (OPI) No. 19200/79 or U.S. Pat. No. 4,220,117 can be employed in which a vapor flow of a magnetic material which has been heated by irradiation with electron beams is directed and deposited onto a moving tape-like non-magnetic substrate (the term "OPI" used herein means a "published unexamined Japanese Patent Application"). The vacuum deposition type magnetic recording medium thus produced provides higher output than the conventional coating type magnetic recording medium and is extremely suitable as a magnetic tape for 8 mm VTR or digital audio equipment. In the vacuum deposition type magnetic recording medium, in order to reduce the noise and to further improve the S/N ratio, an oxidizing gas such as oxygen is introduced during the deposition of the magnetic material as described in U.S. Pat. No. 4,450,186. However, by the introduction of an oxidizing gas, the magnetic properties of the magnetic recording medium, particularly (dB/dH).sub.max (the maximum value of the differential value of the magnetization curve), are deteriorated, improvement in this respect is desirable. Furthermore, the vacuum deposition type magnetic recording medium produced by the conventional electron beam heating process does not provide a sufficient reproduction stability in the envelope of reproduced waves of video signals, especially high frequency signals, and improvement in this respect also has been desired.